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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

GIACIATION OF THE YAKUTAT BAY REGION                 225
Distance from Shore                                                                                Depth
8-8 mile.....................................................    222 feet
1-2   ".....................................................    216   "
6-8   "   .....................................................    321   "
8-4   "   .....................................................    390   "
Because of the steep-sided character of the fiords in these sections, the deltas slope so steeply into deep water that sand should not be found very far offshore.
In outer Yakutat Bay, where we have both soundings and bottom determinations, the Coast Survey chart shows sand in depths of 27 to 30 feet off the borders of the big alluvial fans of Malaspina Glacier. The designations "rocky" and "small stones" are used in certain places near the mouth of the bay, from which we infer there are submerged moraines. Clay is the material over nearly the whole of the bottom of outer Yakutat Bay, the chart showing blue mud and black mud in a great many soundings in depths of from 120 to 680 feet. There is far more sand near the west than near the east shore, where there are now no great streams adding to the submerged glacial deposits.
Three things stand out in connection with the submarine deposits in Yakutat Bay and they are all related to the glacial character of these sediments. (1) These muds and clays, when consolidated, will make shales of considerable area and great thickness, and there will be far more shale than sandstone; (2) the shales will be largely unoxidized, because so large a proportion of the material was ground by the glacier from unweathered rocks; (3) they will be distinguished from normal shales and may be identified as marine, glacial deposits by the angular, striated pebbles and bowlders scattered through them by floating icebergs. Enormous deposits of this sort are accumulating in Yakutat Bay and its branches, Disenchantment Bay and Russell and Nunatak Fiords, especially near the ice fronts of the Turner, Hubbard, and Nunatak Glaciers and also where the streams from Variegated, Hidden, Butler, Fourth, and smaller glaciers, and Black, Galiano, Atrevida, Lucia, and Malaspina Glaciers are pouring out sediments for submarine glacial deposits. These far exceed in extent the till and bowlder ridges, which rise here and there above the fiord bottom.
CONTRIBUTIONS TO INTEBPRETATION or GLACIAL PHENOMENA
The Yakutat Bay region has given us a number of facts of observation which have a direct bearing upon the interpretation of glacial phenomena in regions of former glacia-tion. It is a region of great existing glaciers, a region from which still greater glaciers have only recently retreated, and a region of cool temperate climate, which has given rise to phenomena more clearly resembling those of the wasting glaciers of the Glacial Period than are observed in the margins of the larger glaciers of the colder frigid zones. To the student of glacial phenomena most of the applications to interpretation of glacial features in other regions will be apparent from a reading of the preceding chapters; but the matter seems of sufficient interest to warrant its specific consideration in a few brief paragraphs.
The Piedmont Condition. Where glaciers descended from mountain valleys upon bordering plains or plateaus, or into broader valleys, they expanded during the Glacial Period, as they do now in Alaska. Piedmont bulbs and piedmont glaciers spread out at the base of the mountains in Switzerland, Germany, Austria, and Italy; they devel-
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